1. Technical Field
This invention relates to the art of reducing or eliminating particulates and nitric oxide emitted from a diesel engine and, more particularly, to technology for direct-injected diesel engines that aims to reduce the emission of NO.sub.x to less than 5 gm/hp-hr and particulates to less than 0.09 gm/hp-hr without exhaust gas after-treatment.
2. Description of Prior Art
The U S. Federal Government has set new standards for emissions from heavy duty diesel engines which will take effect in 1991. Generally, engines having cylinder bore diameters of 95-125 mm are used in trucks covered by such standards. Currently known technology cannot attain such standards for such engines without some form of after-treatment device. An after-treatment device allows the particulates to be trapped by filtering, collected, and periodically oxidized to regenerate the filter. Such devices, at best, are expensive and promote unwanted exhaust back pressure in the system.
Several investigations have been undertaken to isolate the factors which affect the generation (or assist in the reduction of generation) of particulates and nitric oxide. Such studies demonstrate that efforts to reduce NO.sub.x concurrently cause an increase in particulate emissions, and efforts to reduce particulates concurrently cause an increase in NO.sub.x (see Cartellieri and Wachter, "Status Report On A Preliminary Survey Of Strategies To Meet U.S.-1991 HD Diesel Emissions Standards Without Exhaust Gas After-Treatment", SAE Technical Paper Series No. 870342, February 1987; and Wade et al,"Reduction of NO.sub.x and Particulate Emissions In The Diesel Combustion Process", Journal of Engineering For Gas Turbines And Power. Vol. 109, p. 426-433, October, 1987). This interaction makes simultaneous control of both pollutants a difficult task. The Cartellieri paper identifies some factors having potential to simultaneously reduce both pollutants, but failed to say how such factors were to be carried out in practice to achieve such result and the degree to which the combustion process needed to be modified. Thus, the identification of such factors without further practical testing leads one to indefinite conclusions and does not offer a usable solution without further experimentation.
In the Wade et al paper, it was recognized that a leaner air/fuel ratio in the premix zone and in the diffusion zone would be necessary to obtain a simultaneous reduction of the pollutants, but the paper failed to suggest "how" to achieve such leaner air/fuel ratios in such locations, while admonishing that it would be very difficult to achieve practically. Variations in the use of air pressure boosting and fuel injection were modeled, but validation of the model with experimental data was limited to ranges that gave inconclusive and contradictory hopes. The predicted hopes were plotted as separate and independent advances; in reality, to obtain leaner air/fuel mixtures in the premix zone (where NO.sub.x is primarily generated) or diffusion zone (where particulates are primarily generated), such factors must be carried out simultaneously. The knowledge, to date, as represented in this paper, fails to show how to reduce the air/fuel mixture in both zones simultaneously without affecting the overall power of the engine.
Therefore, it is a primary object of this invention to simultaneously reduce both nitric oxide and particulates as a result of in-cylinder combustion by simultaneously (i) increasing the local air/fuel ratio in both the premix and diffusion zones of the combustion chamber, and (ii) reducing the ingress of lubricating oil into such combustion chamber by at least 40% without detrimentally affecting the power and durability characteristics of the engine.
A more particular object of this invention is to reduce the fraction of fuel burned in the premix zone of the combustion chamber, improving mixing of the diffusion zone combustion products with air, and thereby reduce particulates to or below 0.09 gm/bhp-hr or 0.44 gm/kg fuel and reducing NO.sub.x to or below 4.4 gm/bhp-hr or 21.6 gm/kg fuel.